Dc power tool with a safety detection device

ABSTRACT

A DC power tool having an interiorly provided lithium battery element and a charging switch includes a safety protection module to eliminate the risk of circuitry burn-out and other dangers resulting from connecting the power tool to a power supply with unmatched rated voltage and rated current when charging the power tool via use of an adapter.

RELATED APPLICATION INFORMATION

This application claims the benefit of CN 200920233242.X, filed on Jul.17, 2009, the disclosure of which is incorporated herein by reference inits entirety.

BACKGROUND

The subject disclosure relates to DC power tools and, more particularly,to a DC power tool which has a built-in lithium battery device and asafety detection device.

A built-in lithium battery device is widely used in power tools. Thebuilt-in lithium battery device is generally provided with a chargingmodule and is connected with a power supply via an outer power adapterfor charging the built-in lithium battery. While power adaptersgenerally have a uniform standard interface, the rated voltage and therated current of power supplies connectable to power adapters with thesame interface may be different. Therefore, when a user charges thebuilt-in lithium battery device, they may use an inappropriate powersupply which may causes the built-in lithium battery device to ruptureor even explode in severe case.

SUMMARY

The following describes a DC power tool with a safety detection devicefor avoiding a risk that may result from erroneous connection with apower supply. More particularly, the DC power tool is interiorlyprovided with a lithium battery element and a charging switch. The powertool can be connected with a power supply via use of an outer poweradapter and is further provided with a safety protection module. Thesafety protection module is an over-current and over-voltage protectionmodule and the over-current and over-voltage protection module comprisesa locking device. In this manner, the power tool eliminates the risk ofcircuit damage and other dangers resulting from wrongly connecting thepower tool to a power supply with unmatched rated voltage and ratedcurrent when seeking to charge the lithium battery element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative diagram of an exemplary charging circuitmodule of a power tool constructed according to the description thatfollows; and

FIG. 2 is an illustrative diagram of an exemplary over-current andover-voltage protection module of the charging circuit of FIG. 1.

DETAILED DESCRIPTION

Referring to FIG. 1, a charging circuit module 100 of a DC power toolcomprises at least one built-in lithium battery element 1, a chargingswitch 2, and an outer adapter 4 connected to the charging switch 2. Thecharging circuit module 100 further comprises a safety protection moduleconnected to the charging switch 2 and the adapter 4. In the presentembodiment, the safety protection module is an over-current andover-voltage protection module 3. The adapter 4 can charge the powertool when connected to an outer power supply with the charging switch 2on.

Referring to FIG. 2, the over-current and over-voltage protection module3 of the present embodiment comprises a current reference 31, and theprotection module 3 contains a current sampling circuit 32. The value ofthe current reference 31 can be predetermined so that when the chargingcurrent is larger than the predetermined value, the voltage of thesampling circuit 32 is increased, and the voltage of the samplingcircuit 32 and the reference voltage are superposed to form anover-current signal 33. The protection module 3 can contain a voltagereference 34. The value of the voltage reference 34 can be predeterminedso that, when the voltage of the adapter 4 is larger than thepredetermined value, an over-voltage signal 35 is generated. After theover-current or over-voltage signal is output via an OR gate 37, alocking device 36 locks the output and a protection signal 38 controlsthe charging switch 2 to interrupt the charging circuit to stopcharging. The locking is released when the adapter 4 is removed. In thisway, the described system eliminates the risk of causing damage to thecircuit and other dangers resulting from wrongly connecting the adapterwith a power supply having unmatched rated voltage and rated current.

While the foregoing describes a preferred embodiment, it will beunderstood that the safety protection module may only comprise anover-current protection device or an over-voltage protection device.Indeed, the safety protection module may comprise an overheatingprotection module to satisfy specific requirements. It will therefore befurther appreciated that present invention is not intended to be limitedto the embodiment disclosed in the description and the drawings and thatother embodiments are also feasible. As such, it is to be understoodthat other alternations which are apparent to the person skilled in theart should be regarded as falling into the protection scope of theclaims that follow.

1. A DC power tool having an interiorly provided lithium battery elementand a charging switch connectable to an exterior power supply whereinthe DC power tool further comprises a safety protection module.
 2. TheDC power tool of claim 1, wherein the safety protection module is anover-current and over-voltage protection module.
 3. The DC power tool ofclaim 2, wherein the over-current and over-voltage protection modulecomprises a locking device.
 4. The DC power tool of claim 1, wherein thesafety protection module is an over-current protection module.
 5. The DCpower tool of claim 1, wherein the safety protection module is anover-voltage protection module.
 6. The DC power tool of claim 1, whereinthe safety protection module is an overheating protection module.
 7. ADC power tool having an interiorly provided battery element and acharging switch for controlling a charging process and an outer adapterconnectable to a power supply in the charging process wherein the DCpower tool further comprises a safety protection module electricallyconnected to the charging circuit for providing safety protection andwherein the safety protection module comprises: a current samplingcircuit connected to the battery element to detect a current provided tothe charging circuit, and a current reference circuit to provide apredetermined current value; wherein an over-current signal is generatedwhen the charge provided to the charging circuit is detected as beinglarger than the predetermined value to turn off said charging switch. 8.The DC power tool of claim 7, wherein the safety protection modulefurther includes a voltage reference circuit to provide a predeterminedvoltage value and to generate an over-voltage signal to turn off thecharging switch when a voltage value provided to the charging circuitlarger than the predetermined voltage value is detected.
 9. The DC powertool of claim 8, wherein the over-current signal and over-voltage signalare transferred to turn off the charging switch via an OR-gate.
 10. TheDC power tool of claim 9, wherein the safety protection module furtherincludes a locking device to lock an output of the OR-gate.
 11. The DCpower tool of claim 7, wherein the safety protection module furtherincludes an overheating protection module for generating an overheatingsignal when a temperature value in the charging circuit higher than apredetermined temperature value is detected to turn off the chargingswitch.
 12. The DC power tool of claim 8, wherein the safety protectionmodule further includes an overheating protection module for generatingan overheating signal when a temperature value in the charging circuithigher than a predetermined temperature value is detected to turn offthe charging switch.
 13. The DC power tool of claim 9, wherein thesafety protection module further includes an overheating protectionmodule for generating an overheating signal when a temperature value inthe charging circuit higher than a predetermined temperature value isdetected to turn off the charging switch.
 14. The DC power tool of claim10, wherein the safety protection module further includes an overheatingprotection module for generating an overheating signal when atemperature value in the charging circuit higher than a predeterminedtemperature value is detected to turn off the charging switch.